Thumb code size diagnostics

In Thumb code, some instructions, for example a branch or LDR (PC-relative),
can be encoded as a 32-bit or 16-bit instruction. The assembler
chooses the size of the encoded instruction as described in Instruction
width selection in Thumb.

The assembler can issue warnings when an instruction is assembled
to a 32-bit Thumb instruction where a 16-bit Thumb instruction could
have been used. To enable this warning, use the following command
line option when invoking the assembler: